This invention relates to bisphenol chemistry, and more particularly to the preparation of a genus of catalysts containing bisphenol moieties.
The use of tetraalkylammonium and hexaalkylguanidinium salts as phase transfer catalysts in the preparation of various polymers is known. In particular, U.S. Pat. Nos. 4,273,712 and 5,132,423 disclose the reaction of bisphenol salts with halo- or nitro-substituted phthalimides in an organic medium to produce bisimides which, upon conversion to dianhydrides and reaction with diamines, form polyetherimides. U.S. Pat. Nos. 3,787,364, 3,838,097, 3,847,869 and 5,229,482 disclose a similarly phase transfer catalyzed reaction of bisphenol salts with halo- or nitro-substituted bis(phthalimido) derivatives of aromatic diamines or with similar compounds, resulting in the direct formation of polyetherimides and other polyether polymers. The phase transfer catalysts employed according to U.S. Pat. Nos. 5,132,423 and 5,229,482 are guanidinium and especially hexaalkylguanidinium salts; in the other patents, tetraalkylammonium salts are disclosed as suitable catalysts.
The hexaalkylguanidinium salts which are easiest to prepare are the chlorides, but they are hygroscopic. It is burdensome to store them in anhydrous form and subsequently dry them or to isolate them in anhydrous form, which is essential for the polyetherimide-forming reactions.
One of the by-products in the reaction of bisphenol salts with nitro-substituted compounds is an alkali metal nitrite, typically sodium nitrite. It is ordinarily removed by washing the organic reaction system with water. It would be desirable to recover the sodium nitrite and sell it for further use.
However, chloride levels in by-product nitrite salts are high, which can cause corrosion of metal reaction vessels in contact therewith. In addition, commercial applicability requires that sodium nitrite contain a very low chloride level, typically no greater than 100 ppm by weight, which is difficult or impossible to attain with the use of a hexaalkylguanidinium chloride, for example, as a phase transfer catalyst.
For these reasons and others, it is desirable to prepare non-hygroscopic hexaalkylguanidinium and tetraalkylammonium salts, as well as salts containing an anion other than chloride.